Si-Ge heterostructures made of 6 monolayers of Si and 4 monolayers of Ge repeated p times (Si6Ge4)(p), strained on Si (1 0 0) substrates, have been investigated by photoluminescence measurements and electron microscopy. The films were grown at 400 degrees C by molecular beam epitaxy, using Sb as surfactant. The photoluminescence results of the whole set of samples show similar spectra, for both the single Ge quantum well (p = 1) and the thicker heterostructure (p = 30). The phonon assisted transverse optical line is measured at about 40 meV far from the no-phonon one, and this corresponds to the Ge-Ge vibration. Our results demonstrate that excitonic recombination occurs mainly in the Ge layers and it is indirect in nature, whatever the repetition number (p) is. Furthermore, we evidenced a high localization of the photoluminescence process excluding any superperiodicity effect.
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